The present invention relates generally to water regeneration or recovery from wastewater and more particularly, to water regeneration by cascade distillation.
One of the most important resources for human support is potable water. Since fresh potable water cannot be supplied for long duration space missions recovery of wastewater is essential. Wastewater generally consists of urine, hygiene water, and humidity condensate. A wastewater processing system converts the wastewater to potable water fit for long-term human consumption. The reliable and effective operation of the wastewater processing system is a major consideration for design and operation of the life support system. The important features of a wastewater processing system are potable water quality, water processing rate, water recovery efficiency, specific energy consumption, consumable use, and installed size and weight.
The water processing system for use on spacecraft is complex and usually consists of a number of components including pumps, tanks and controls. Wastewater is purified in a primary processor followed by a secondary processor and finally a water polisher to insure that the water quality is at spacecraft potable standard. Water processing systems using a number of different technologies have been developed or are under investigation.
One important technology is the use of distillation. As an element in a complete water recovery system distillation units are used to recover water from urine and brines. Water processing systems must have a function to remove mineral salts. Wastewater, especially human urine, contains mineral salts that must be removed if the recycled water is to become potable. The result of distillation is purified water and concentrated brine.
Vacuum rotary distillation processors compare favorably with other distillation processors for use in spacecraft water processing systems. Vacuum distillation technology has been in development for over 26 years. Excellent performance of this technology for urine processing has previously been demonstrated. U.S. Pat. No. 6,258,215 describes a system including rotary multi-stage vacuum distiller for recovering water from urine. However the rotary distiller of the '215 patent has insufficient construction seals so that there is a high risk of contamination of product water by wastewater. Moreover, the '215 patent only describes a system to be used in microgravity and only for recovering water from urine to the exclusion of other aqueous waste.
U.S. Pat. No. 6,695,051 describes the use of vapor compression distillation for the production of water from wastewater. Vapor compression distillation requires a steam compressor and the boiling of the liquids. With wastewater having a high mineral and salt content, such as urine, the boiling of the liquid leaves mineral and salt deposits on the apparatus, resulting in decreased lifetime of the apparatus. Vapor compression distillation also uses a significantly higher amount of energy per kg of water produced.
As can be seen, there is a need for an apparatus and method for producing water from wastewater, especially urine, which is lightweight, uses a minimal amount of energy and limits the cross-contamination of the wastewater with the purified water.